Common deposits in aqueous medium include iron oxides, calcium and magnesium carbonates, sulfates, oxalates, and phosphates, as well as silt, alumina, aluminum silicates, and clays. Environments where some of the deposition problems are often encountered range from silt and mud accumulation in bottoms of water storage tanks and ballast tanks of vessels and on ships, to the fouling problems which occur in water cooling systems using the once-through or recirculating systems and to deposition problems which would occur in cooling and boiler water systems if the water were not treated beforehand.
If all particulate matter could be kept dissolved or at least maintained in suspension, if already in solid state, there would never be any deposition problems to contend with. The phenomenon of suspension involves settling of particles in a liquid medium. The parameters which control settling rates are particle size and relative density of liquid and particles. However, once particles have settled, the nature of the resulting sludge is dependent on the attractive forces between the particles and the surfaces which they contact. If the attractive forces between particles are strong, the formed deposit will be dense but if the attractive forces between the particles are weak, deposition is less likely to occur, particularly at flow conditions.
U.S. Pat. Nos. 3,709,815 and 3,709,816 are directed to boiler water treatment and to control of alluvial and other deposits in aqueous systems by the use of homopolymers and copolymers of acrylamido-alkane sulfonic acid, such as 2-acrylamido-2-methylpropane sulfonic acid or AMPS. The comonomers are selected from water-soluble and water-insoluble monomers. Suitable comonomers include acrylic acid, variants and salts thereof and acrylamide, variants and substituted forms thereof, as well as alkali metal styrene sulfonates and vinyl benzoates, and others. The particulates encompassed by these patents include clay, silt, calcium carbonate, hydrated ferric oxide, silica, magnetic iron oxide, calcium carbonate, magnesium carbonate, aluminum silicate, and the like.
U.S. Pat. Nos. 3,806,367 and 3,898,037 issued from the same patent application. U.S. Pat. No. 3,806,367 is directed to the removal of rust and tubercules from a metal surface whereas U.S. Pat. No. 3,898,037 relates to inhibition of corrosion of a metal surface which is in contact with an aqueous solution. These patents disclose the use of dispersants which are homopolymers and copolymers of acrylamido-alkane sulfonic acid, such as 2-acrylamido-2-methyl propane sulfonic acid or AMPS.RTM.. The copolymers can be polymers of two or three monomers, one of which is an acrylamidoalkane sulfonic acid. Suitable comonomers include acrylic acid, salts thereof and other versions of same; acrylamide and substituted versions thereof; vinyl compounds; vinyl acids and esters thereof; and the like. The comonomers are more fully described in col. 5 of U.S. Pat. No. 3,898,037.
The Amick U.S. Pat. No. 4,711,725 discloses stabilization of an aqueous system by inhibiting precipitation of calcium phosphate with a copolymer antiscalant, said copolymer comprising 42 to 84% of (meth)acrylic acid and salts thereof, 11 to 40% acrylamido alkane sulfonic acid, and 5 to 30% of one or more monomers selected from vinyl esters, vinyl acetate, and substituted acrylamides. The aqueous medium can contain or can be devoid of iron contamination.
The other patent applications concurrently filed for Messrs. Amjad and Masler include one entitled "Scale Control With Copolymers Containing Acrylamidoalkane Sulfonic Acid" and another entitled "Stabilization of Metal Ions With Copolymers Containing Acrylamidoalkane Sulfonic Acid". These cases disclose the use of same or similar polymers.